1. Field of the Invention
This invention relates to a check valve made of plastic used for dispensing a fluid from a container.
2. Description of Prior Art
Such valves are often used with foil containers for liquids, and in turn are placed into cardboard boxes. This type of packaging is known by the phrase "bag-in-box". The advantages of such packaging are low weight, easy stacking, avoidance of transporting the empty container and low price compared with glass containers or metal drums.
It follows that the check valve for pouring liquid provided with such packaging must also be of low cost. For this reason valves made of plastic are generally used, which can be easily connected with, and in particular affixed to, the foil of the container. Besides different, multi-part, complex and expensive solutions, some simple solutions are also known.
U.S. Pat. No. 4,375,862, for example, discloses a rather complicated check valve which is designed as a plug-in valve. A flange welded to the plastic bag is seated in the cardboard packaging. A plug housing with a central plug, whose end toward the container is closed by a sealing peg which can be pushed out, is sealingly seated in the flange. A multi-part plug can be pushed into the plug housing, where it locks together with the sealing peg and pushes it into the container. The actual opening or closing position is achieved by turning the plug in the plug housing. Such a valve only permits small flow-through openings and the fluid path between the sealing point and the outlet opening at the end is very long. Accordingly, such a valve is only suited for very mobile containers, and dripping of the liquid long after the valve has been closed is unavoidable.
A valve which is particularly simple and includes only a few components is disclosed by Australian Reference 403,943. Here, the valve body is essentially a cylindrical connector with a flange on the inlet side with which the plastic container is connected, and with a diaphragm sealing the end on whose inside a push rod is disposed. A valve plate, which in the closed state rests on the valve seat in the valve body, is seated on the push rod. With pressure applied to the flexible diaphragm, the rod pushes the valve plate inside the valve body away from the valve seat. The liquid flows around the valve plate and by a radial outflow bore reaches the outside in the area between the valve seat and the sealing, flexible diaphragm. The valve plate remains always inside the valve body and constitutes a constant obstacle to the flow during opening. Dripping occurs for a relatively long time after the valve is closed, until the void behind the valve plate has been completely emptied. A further embodiment is disclosed in the same reference, wherein the plate has been replaced by a linearly displaceable plug with a flow-through opening. In the closed position the lateral wall of the linearly displaceable sealing plug lies across the radial outflow opening in the valve body. The flow paths in this valve are also disadvantageous and sealing is questionable, in particular the second embodiment discussed.
Two similar check valves of the same applicant are known from the two U.S. Pat. Nos. 4,471,807 and 4,452,425, both of which have a similar design. These check valves made of plastic include a valve housing with an inlet connector and an outlet opening which serves as a valve seat, and a linearly displaceable movable valve sealing body which can be moved away from the valve seat by a push rod. The pressure of the liquid on the side of the push rod acts on the valve plate. The great advantage of such valves is that the valve sealing body directly closes off the outlet opening, since the outlet opening serves as the valve seat. Accordingly, there is almost no post-dripping of the liquid. However, it is disadvantageous that the liquid rests against the push rod side of the valve plate and that the valve plate is displaced in the direction of the applied pressure during opening. A potential interior pressure could open the valve accidentally. Furthermore, the push rod is moved in the opening direction by a flexible diaphragm. Unintended pressure on this exposed diaphragm therefore causes an unwanted opening of the valve.
U.S. Pat. No. 4,471,807 discloses a solution to the first mentioned problem. A valve plate on the inlet side of the opening is displaced away from the opening and into the interior of the container by a reversing mechanism acting on the push rod. This complicates the closure and reduces the flow-through of the fluid.
U.S. Pat. No. 4,452,425 discloses a simple solution to the second problem by positioning a protective cap over the flexible diaphragm. The cap must be removed prior to each use. However, both solutions still have certain structural disadvantages. One disadvantage is that the interior pressure in the container is not used for closing the valve. Another disadvantage is that the push rods lie in the outlet opening when the valve is opened and therefore reduce the free cross-sectional outflow area. Yet another disadvantage is that the actual valve sealing body lies directly in the stream of the evacuating fluid, which can spray uncontrollably in all directions.